High surface area aggregated pigments

ABSTRACT

Aggregated mineral pigments (such as kaolin clay pigments) having a high surface area and useful in coating compositions for ink jet printing media are manufactured by dry grinding an unground mineral composition starting material and then optionally acid treating the ground material.

TECHNICAL FIELD

This invention relates to aggregated pigments having a low lightscattering coefficient and a high surface area. In a more specificaspect, this invention relates to aggregated pigments which have a highsurface area and a low light scattering coefficient and which are usefulin coating compositions for ink jet printing media. This invention alsorelates to a process for the manufacture of these aggregated pigments.

This invention will be described in detail with specific reference tokaolin clay. However, this invention will be understood as applicable toother mineral compositions, such as natural calcium carbonate,precipitated calcium carbonate, calcium sulfate (normally known asgypsum), bentonite, talc, aluminum oxide and aluminum hydroxide.

BACKGROUND OF THE INVENTION

Kaolin is a naturally occurring, relatively fine, white clay mineralwhich may be generally described as a hydrated aluminum silicate. Afterpurification and beneficiation, kaolin is widely used as a filler andpigment in various materials, such as rubber and resins, and in variouscoatings, such as paints and coatings for paper.

The use of kaolin in paper coatings serves, for example, to improvebrightness, color, gloss, smoothness, opacity, printability anduniformity of appearance of the coated paper. As a filler in paperformulations, kaolin is used to extend fiber and reduce cost, and toimprove opacity, brightness and other desirable characteristics of thefilled paper product.

Calcined kaolin is a particular type of kaolin and is often used inlarge quantities for paper manufacture. Calcined kaolin can be obtainedby heating (i.e., calcining) beneficiated kaolin clay at temperatures ofat least 550° C. The calcination step dehydroxylates and converts thekaolin into a noncrystalline aluminosilicate phase or metakaolin. Theterm “dehydroxylates” refers to the removal of structural hydroxylgroups from the kaolin in the form of water vapor. The smaller particlesof the feed clay are aggregated by calcination, and this aggregationincreases the original volume of the kaolin and gives the calcinedkaolin a “fluffy” appearance. Particle aggregation increases the lightscattering characteristics of the kaolin (as compared to non-calcinedkaolin) and, therefore, contributes a high degree of opacity to a coatedpaper. In addition, calcination increases the brightness of the kaolin.

Fanselow et al. U.S. Pat. No. 3,586,523 describes calcined kaolin clays.

Calcined kaolin clay pigments (such as those marketed by Thiele KaolinCompany of Sandersville, Georgia under the trademarks KAOCAL and KAOCALLA) are widely used in the paper industry. The high brightness of thecalcined clay is partly due to the removal of organic material atelevated temperatures. The brightness can also be improved throughpre-calcination beneficiation processes such as magnetic separation,froth flotation, selective flocculation and chemical leaching.

Hydrous kaolin clay is another conventional product (such as thatmarketed by Thiele Kaolin Company under the trademark KAOFINE 90) whichis widely used in the paper industry. This particular type of kaolin hasnot been subjected to a calcination step.

Both hydrous and calcined clay products are useful in coatingcompositions for conventional printing applications such as offset,rotogravure, letterpress and flexographic. However, without substantialmechanical and/or chemical modifications, hydrous and calcined clayproducts are not useful in coating compositions for ink jet printingapplications.

In an ink jet printing process, uniformly shaped tiny droplets ofaqueous or solvent based dye solutions are ejected from a nozzle onto asubstrate. There are two primary types of ink jet printing - continuousink jet printing and drop on demand ink jet printing (DOD). Thecontinuous ink jet is used in high speed printing such as addressing,personalization, coding and high resolution color printing such asproofing. The DOD ink jet is mainly used in home, office and wide formatprinting.

The thermal ink jet printer is the most common DOD ink jet currentlyavailable. In this system, ink is heated and vaporized periodically witha heating element connected to the digital data to generate bubbles.Since the volume of the ink increases during vaporization, the ink isforced out of the nozzle in the form of a drop which travels and isdeposited on the paper.

The inks used in ink jet printing are commonly dilute solutions ofwater-soluble organic dyes. The solvent portion of these inks can be ashigh as 98% and is a mixture of water and high boiling point alcohols.Many of the dyes used in ink jet printing inks contain sulfonic andcaboxylic acid groups. At the pH of the ink, these groups are ionizedand become anionic. Once deposited on the substrate, the ink must dryquickly to avoid spreading to the adjacent printing pixel. Because ofthe large amount of solvent used in ink jet inks, the coating must besufficiently absorbent to remove the solvent away from the surface sothat the inks will not smear. At the same time, for sharp edge acuity,the coating must fix the dye in the ink on the surface with no lateralspreading.

There are three major requirements for pigments/coatings to provide goodink jet printing characteristics: (1) high surface area and porosity forrapid absorption of the ink liquid, (2) cationic surface charge toquickly fix or immobilize the anionic ink jet dyes on the surface of theprinted substrate and (3) low light scattering which improves the colorof the printed image by not diluting the colors as the ink penetratesinto the printed substrate.

Currently, silica is the pigment of choice for ink jet coating. Silicaenhances ink jet printing by virtue of its high surface area (>150 m²/g)and porosity. However, silica is much more expensive than conventionalpigments based on kaolin or calcium carbonate. Also, silica imparts highviscosity to the coating and cannot be made down at high levels ofcoating solids. Because of the viscosity/solids issue with silica, thecoating machines cannot be integrated with paper making machines andconsequently must be operated off line. This off line situationeffectively reduces the productivity of the paper mills.

Several non-silica based pigments for ink jet paper coating applicationshave recently been introduced. For example, heat aged precipitatedcalcium carbonate with a surface area of at least 60 m²/g is describedin Donigan et al. U.S. Pat. No. 5,643,631. This material is claimed toreduce feathering, spreading and penetration or backside show through,as well as improve optical density, dry time and water fastness.

Chen et al. PCT International Publication No. WO/98/36029 and Chen etal. U.S. Pat. No. 6,150,289 describe a coating composition comprising100 parts calcined clay, 5-50 parts by weight of a cationic polymer,20-30 parts by weight polyvinyl alcohol, 30-50 parts by weight of alatex binder and 0-5 parts by weight of a cross-linking agent.

Londo et al. U.S. Pat. No. 5,997,625 describes a coating compositioncomprising a fine particle hydrous clay, a caustic leached calcined clayand a porous mineral (zeolite). This composition exhibits the bestoverall color density and color definition compared with the individualcomponents.

For various reasons, the above described products fail to provide eithercost-effectiveness or performance advantages over the conventionalsilica pigment. Thus, there is a need in the industry for cost-effectivecoating pigments having equivalent or improved printing performance andTheological characteristics over silica for ink jet printing media.

SUMMARY OF THE INVENTION

Briefly described, the present invention provides aggregated pigmentswhich have a high surface area and low light scattering and which areuseful in coating compositions for ink jet printing media. The presentinvention also provides a process for the manufacture of theseaggregated pigments. Again, although described with regard to kaolinclay, the present invention will be understood as applicable to othermineral compositions such as natural calcium carbonate, precipitatedcalcium carbonate, bentonite, talc, aluminum oxide and aluminumhydroxide.

As used in this application, the term “high surface area” refers to thesurface area of the pigments of this invention, and this surface area ishigher (i.e., greater) than the surface area of the starting material.Likewise, the term “aggregated” refers to the morphology of the pigmentsof this invention, which are clusters of a few to several fineindividual particles that are smaller than the original startingmaterial particles. Also, “low light scattering” refers to the lightscattering coefficient of the pigments of this invention, and this lightscattering is lower than the light scattering of the starting material.This aggregated morphology, high surface area and low light scatteringenable the pigments of this invention to be useful in coatingcompositions for ink jet printing media.

As will be seen in greater detail below, the pigments of this inventionhave other characteristics which are either equivalent to or improvedover the corresponding characteristics of silica.

Accordingly, an object of this invention is to provide an aggregatedpigment having a high surface area and low light scattering.

Another object of this invention is to provide an aggregated pigmenthaving a high surface area and low light scattering and which is usefulin coating compositions.

Another object of this invention is to provide an aggregated pigmenthaving a high surface area and low light scattering and which is usefulin coating compositions for ink jet printing media.

Another object of this invention is to provide an aggregated kaolin claypigment having a high surface area and low light scattering.

Another object of this invention is to provide an aggregated kaolin claypigment having a high surface area and low light scattering and which isuseful in coating compositions.

Another object of this invention is to provide an aggregated kaolin claypigment having a high surface area and low light scattering and which isuseful in coating compositions for ink jet printing media.

Another object of this invention is to provide an aggregated mineralpigment having a high surface area and low light scattering.

Another object of this invention is to provide an aggregated mineralpigment having a high surface area and low light scattering and which isuseful in coating compositions.

Another object of this invention is to provide an aggregated mineralpigment having a high surface area and low light scattering and which isuseful in coating compositions for ink jet printing media.

Still another object of this invention is to provide a process for themanufacture of an aggregated pigment having a high surface area and lowlight scattering.

Still another object of this invention is to provide a process for themanufacture of an aggregated pigment having a high surface area and lowlight scattering and which is useful in coating compositions.

Still another object of this invention is to provide a process for themanufacture of an aggregated pigment having a high surface area and lowlight scattering and which is useful in coating compositions for ink jetprinting media.

Still another object of this invention is to provide a process for themanufacture of an aggregated kaolin clay pigment having a high surfacearea and low light scattering.

Still another object of this invention is to provide a process for themanufacture of an aggregated kaolin clay pigment having a high surfacearea and low light scattering and which is useful in coatingcompositions.

Still another object of this invention is to provide an aggregatedkaolin clay pigment having a high surface area and low light scatteringand which is useful in coating compositions for ink jet printing media.

Yet still another object of this invention is to provide a process forthe manufacture of an aggregated mineral pigment having a high surfacearea and low light scattering.

Yet still another object of this invention is to provide a process forthe manufacture of an aggregated mineral pigment having a high surfacearea and low light scattering and which is useful in coatingcompositions.

Yet still another object of this invention is to provide a process forthe manufacture of an aggregated mineral pigment having a high surfacearea and low light scattering and which is useful in coatingcompositions for ink jet printing media.

These and other objects, features and advantages of this invention willbecome apparent from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the scanning electron micrograph of the unground Kaofine 90starting material used in Example 1.

FIG. 2 shows the scanning electron micrograph of the ground Kaofine 90product described in Example 2.

FIG. 3 shows the scanning electron micrograph of the unground Kaocalstarting material used in Example 4.

FIG. 4 shows the scanning electron micrograph of the ground Kaocalproduct described in Example 4.

FIG. 5 shows the scanning electron micrograph of the natural calciumcarbonate starting material used in Example 5.

FIG. 6 shows the scanning electron micrograph of the calcium carbonateproduct described in Example 5.

FIG. 7 shows the scanning electron micrograph of the precipitatedcalcium carbonate starting material used in Example 6.

FIG. 8 shows the scanning electron micrograph of the precipitatedcalcium carbonate product of Example 6.

FIG. 9 shows the scanning electron micrograph of the unground talcstarting material used in Example 8.

FIG. 10 shows the scanning electron micrograph of the ground talcproduct described in Example 8.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a mineral pigment (such as kaolin clay,calcined kaolin clay, calcium carbonate, bentonite, talc, aluminumhydroxide or aluminum oxide) having a high degree of aggregation, highsurface area and low light scattering coefficient, which is produced bya process comprising the sequential steps of (A) obtaining abeneficiated, unground mineral composition starting material; and (B)dry grinding the starting material under conditions of high intensity,whereby the ground ultrafine particles are aggregated to yield a productthat is increased in surface area and decreased in light scatteringcoefficient over those characteristics of the unground startingmaterial.

The present invention also relates to a process for the manufacture of amineral pigment (such as kaolin clay, calcined kaolin clay, calciumcarbonate, bentonite, talc, aluminum hydroxide or aluminum oxide) havinga high degree of aggregation, high surface area and low light scatteringcoefficient, wherein the process comprises the sequential steps of (A)obtaining a beneficiated, unground mineral composition startingmaterial; and (B) dry grinding the starting material under conditions ofhigh intensity, whereby the ground ultrafine particles are aggregated toyield a product that is increased in surface area and decreased in lightscattering coefficient over those characteristics of the ungroundstarting material.

In this application, the term “unground” refers to a mineral compositionwhich has not been subjected to dry grinding under conditions of highintensity.

The preferred mineral composition starting material for this inventionis hydrous kaolin clay, calcined kaolin clay, bentonite, natural calciumcarbonate, precipitated calcium carbonate, calcium sulfate, talc,aluminum hydroxide, aluminum oxide or a mixture of two or more of theseminerals.

As discussed earlier, a highly absorbent pigment (that is, a pigmenthaving a high surface area and high porosity) is necessary for ink jetcoating to remove the ink solvent rapidly away from the surface (alsoreferred to as ink drying). However, the surface area of hydrous kaolinclays ranges from 5-25m²/g, which is lower than the ˜150-600 m²/gsurface area of a silica pigment. Because of the lower surface area,hydrous kaolin clays are not suitable pigments for coating ink jetprinting paper. However, we have found that hydrous kaolin clay, aftercontrolled high intensity dry grinding, improves ink drying, imageformation (also referred to as image acuity) and color density over theoriginal unground hydrous kaolin clay.

These improvements in ink drying and image formation of the pigments ofthis invention are due to the increases in porosity, pore size andsurface area. The increases in porosity and pore size (as measured byMercury Porosimetry) can be attributed to an increase in particle sizeas a result of particle aggregation. Normally, as particle sizeincreases, surface area is expected to decrease. However, in the presentinvention, the particle size first decreases as a result of a very highimpact of the grinding media. The broken fine particles are thenaggregated to form larger particles. The high surface area of the groundproducts indicates that the aggregates are not very dense, and nitrogenmolecules used in measuring the surface area detect the high surfacearea of the fine particles.

As mentioned above, the intense dry grinding process increases pore sizebeyond what is optimum or near optimum for light scattering.Consequently, the light scattering coefficient of most of the pigmentproducts of this invention is reduced, especially the starting materialsthat have a relatively high scattering coefficient (>0.35). The reducedlight scattering coefficient, in turn, improves the color density of theprinted image by not diluting the color as the ink penetrates into thecoated sheet. However, prolonged grinding should be avoided since suchgrinding increases particle size with concomitant increases in the 325mesh screen residue as a result of large and hard agglomeration of theparticles. Also, prolonged grinding will require more energy, therebyincreasing the cost of production, while not improving the productquality.

A calcined clay coating is improved in ink drying over hydrous clayproducts because of the high porosity of the calcined clay. However,having a relatively low color density as compared to hydrous clay,calcined clay is not suitable for ink jet coating applications. Asdiscussed above, the lower color density of calcined clay can beattributed to its high light scattering ability.

By controlled intense dry grinding, we have found that the lightscattering coefficient of calcined clay can be reduced significantly andthe color density of the printed image can be improved over that of theoriginal calcined clay. Like hydrous clay, the ground calcined clay isheavily aggregated with increases in surface area and pore size,although >50% of the original pore volume (i.e., porosity) is lost aftergrinding. The decrease in pore volume and increase in pore size aftergrinding are responsible for the reduced scattering coefficient ofground calcined clay. Despite the reduction in pore volume, theremaining porosity of the aggregated product is sufficient to providerapid ink drying of the printed image.

Natural and precipitated (i.e., synthetic) calcium carbonate pigmentsare widely used in conventional paper coating and/or fillingapplications. These pigments are also not suitable for ink jet coatingapplication due to poor ink absorption and poor image formation.However, this invention can significantly modify the properties of thesepigments to make them useful in ink jet coating applications. As withhydrous kaolin, this invention increases aggregation (particle size),porosity, pore size and surface area and decreases light scatteringcoefficient as compared to the starting feed material.

Bentonite is not used in paper coating, but it is used in smallquantities in paper making processes as a deinking agent, pitch controlagent and retention aid. Bentonite is a rock term used to describe anaturally occurring fine-grained material predominantly composed of themineral smectite. Smectite is a 2:1 hydrous layer aluminosilicatecontaining various alkali and alkaline earth metal cations in theinterlayer. Smectites are further classified into beidellite,nontronite, saponite and montmorillonite depending on their crystalchemical characteristics. As with calcium carbonate, bentonite can alsobe ground at high intensity to yield a aggregated high surface areapigment suitable for ink jet coating applications.

Talc is used in small quantities in paper coating and fillingapplications. Talc refers to a hydrous layer magnesium silicate mineral.Normally, talc used in paper coating applications is much coarser thankaolin clays. Like other minerals described above, dry grinding at highintensity yields an aggregated high surface talc product suitable forink jet coating applications. Because of the very coarse particle sizeof the starting talc (unlike clay, calcium carbonate and bentonite),talc requires higher grinding intensity or retention time to achieve adesirable degree of aggregation for ink jet coating applications.

We have also found that treating the ground clay with a mineral ororganic acid can further increase the surface area of the pigment. Forexample, the surface area of ground kaolin clay increases from ˜40 m²/gto ˜150 m²/g when treated with 1 M sulfuric acid at 90° C. for 4 hr. Thesame treatment only increases the surface area of the original ungroundclay from 20 m²/g to 24 m²/g.

Most of the high brightness calcined clays are fully calcined products.By fully calcined, we mean the product is calcined beyond its exothermictemperature (>980° C.). As true with hydrous clay, the fully calcinedclay does not show a high surface area after acid treatment. On theother hand, the surface area of a clay which has been calcined at alower temperature (referred to as metakaolin) increases many times afteracid treatment, but the printed color density of this product is verylow due to its high scattering coefficient. However, after highintensity grinding, both the fully calcined clay and the low temperaturecalcined clay can be acid treated to yield high surface area pigmentsand provide coatings with good color density, adequate ink absorption,adequate ink drying and good image formation.

The present invention is further illustrated by the following exampleswhich are illustrative of certain embodiments designed to teach those ofordinary skill in the art how to practice this invention and torepresent the best mode contemplated for carrying out this invention.

Examples 1 and 2 show that high surface area and highly aggregatedproducts can be produced by dry grinding of hydrous clay. These examplesalso demonstrate that the grinding conditions need to be optimized toproduce a product suitable for ink jet coating applications.

EXAMPLE 1

A high brightness Fine No. 1 clay marketed under the trademark KAOFINE90 (KF90) by Thiele Kaolin Company is used as the starting material.This product is dry ground continuously at varying feed rates using alaboratory high-speed attritor (Model HSA-1, Union Process Co., AkronOhio) at a stirring speed of 1100 RPM with 2000 ml of zirconium silicatemedia (2.0-2.5 mm beads) and a discharge screen of 0.6 mm (100% open).The BET surface area and Sedigraph particle size distributions arepresented in Table I. The data indicate that the surface area andparticle size are increased with decreases in feed rate. The lower thefeed rate, the higher is the grinding intensity. As the grindingintensity increases, the clay particles are broken down into ultrafineparticles, which are then aggregated almost instantly to increase theparticle size.

Ground samples are evaluated for ink jet coating and printability.Pigments are made down at 60% solids using a Premier mixer under highshear (˜4000 RPM). Coating formulations are prepared at 44-46% solids bymixing 15 parts per hundred (pph) of polyvinyl alcohol binder to theanionically dispersed pigment slurry (8 Lb/T of sodium polyacrylate onan active basis). The coatings are applied to a substrate having a basisweight of 70 m²/g using a manual draw down machine on one side. Thecoated sheets are dried in a convection oven for 1 minute at 105° C. Thecoat weight is maintained in the range of 8-10 g/m². The Hewlett-Packard(HP) print pattern (Paper Acceptance Criteria for Hewlett-PackardDeskjet 500C, 550C and 560 C Printers, 2^(nd) edition, Hewlett-PackardCompany, 1994) test images are printed with a HP DeskJet 695C printer.The print is visually observed for ink dry-time (time to absorb ink),visual wicking and bleeding. The print color (cyan, magenta, yellow andblack) density is measured using a X-Rite Densitometer Model #418.

The data in Table I show that the products ground at 6.5 Lb/hr and 10.5Lb/hr feed rates perform close to each other in terms of color densityand dry time. Under the same conditions of stirring speed and mediavolume, feed rates greater than or equal to 19.2 Lb/hr results in poorink jet performance in terms of color density and dry-time. This ispresumably due to a lower degree of aggregation at the higher feed rateswhich results in a lower porosity of the coating film.

The original Kaofine 90 feed results in a high black ink density but hasa very poor color density and an unacceptable image quality. Ink in thecolor prints is agglomerated, and a poor image is formed. The productground at 36 Lb/hr feed rate performs almost similar to the originalKaofine 90.

TABLE I Original Kaofine 90 Ground at Different Feed Rates Grindingconditions Feed rate, — 36 23 19.2 10.5 6.5 Lb./hr Dry grinding — 1 1 11 1 aid (diethylene glycol), ml/Lb BET Surface 21.7 27.3 29.6 31.7 39.343.4 area Particle size, % <5.0μ 98.5 91.2 87.8 86.5 69.1 64.1 % <2.0μ98.2 81.5 75.7 72.1 49.3 40.0 % <1.0μ 98.2 75.2 67.4 62.9 40 29.7 %<0.5μ 91.9 59.7 50.8 48 28.2 20.4 % <0.2μ 48.0 23.7 17.8 16.6 9.2 7.9Scattering 0.4911 0.4146 0.3809 0.3421 0.2784 0.20 coefficient Ink JetPrintability (Uncalendered) Color density Cyan 1.33 1.34 1.36 1.37 1.431.45 Magenta 1.16 1.22 1.22 1.22 1.32 1.39 Yellow 0.90 0.95 0.94 0.911.02 1.07 Black 1.85 1.37 1.34 1.32 1.30 1.37 Image Very Very Poor PoorGood Good Formation Poor Ink absorption/ 5 5 5 4.0 3.5 3 dry* *1 = bestand 5 = worst

This example demonstrates the effects of stirring speed and grindingmedia volume on the physical properties of the ground products and theirink jet coating printability performance.

Kaofine 90 is dry ground using the same attritor as in Example 1 with a0.6 mm screen opening (100% open) at 10 Lb/hr feed rate at variousstirring speeds and media volumes. Zirconium silicate of 2-2.5 mm sizeis used as the grinding media. The physical properties and ink jetprintability of the products are given in Table II.

TABLE II Original Feed Ground KF 90 Products (KF 90) I II III IV VGrinding Conditions Stirring Speed — 1000 1100 1100 1200 1350 (RPM)Media Volume — 1600 2000 2400 2400 2400 (ml) Surface area 21.7 37.3 46.649.4 40.9 29.7 (m²/g) Particle size % <5 μm 98.5 75.5 63.4 59.8 61.163.8 % <2 μm 98.2 56.7 41.3 35.5 34.5 34.9 % <1 μm 98.2 45.9 31.1 24.023.3 22.7 % <0.5 μm 91.9 33.0 21.8 16.7 15.9 15.1 % <0.2 μm 48.0 10.26.9 5.6 4.7 5.9 Ink Jet Printability (Soft Nip Calendered @ 1 Nip/side,55 PLI at 160° F.) Color Density Cyan 1.36 1.46 1.54 1.58 1.58 1.61Magenta 1.24 1.29 1.44 1.45 1.45 1.52 Yellow 0.94 1.02 1.12 1.18 1.181.25 Black 2.01 1.28 1.28 1.28 1.29 1.26 Image Very Poor Good Good GoodGood Formation Poor Ink drying* 5 5 3 3 3 3 *1-best and 5-worst. PLI =Pressure per Linear Inch

The data in Table II show that the particle size increases and thenlevels off with stirring speed and/or media volume. The particle sizeincreases as a result of the aggregation of ultrafine particles. Thiscan also be seen in the scanning electron micrographs (FIGS. 1-2). Thesurface area first increases and then decreases with increasing mediavolume and/or stirring speed. The decrease in surface area after initialincrease can be attributed to the formation of harder (more compact)aggregates with increasing grinding intensity. The stirring speed and/ormedia volume results in increased grinding intensity.

The ground samples are evaluated for ink jet coating and printability.Pigment slurries are made down at 60% solids. Coating formulations areprepared at 44-46% solids with 13 pph of polyvinyl alcohol (partiallyhydrolyzed Airvol 21-205 grade from, Air Products & Chemicals, Inc.) and5 pph of poly-DADMAC dye retention agent (cationic polymer of lowmolecular weight and high charge) in each case. The coatings are testedand applied to a base sheet (˜90 gm/m²) using a manual draw downmachine. The coat weight is maintained in the range of 8-10 gm/m². Thecoated sheets are conditioned in a standard humidity room and then softnip calendered (1 Nip/side, 55 PLI at 160° F.) using a laboratorycalender.

The Hewlett-Packard print pattern test images are printed with a HPDeskJet 695C printer. The print is visually observed for ink dry-time(time to absorb ink), print density (cyan, magenta, yellow and black),visual wicking and bleeding. The ink jet print performance improves withincreasing stirring speed and/or media volume.

Examples 3-8 demonstrate that the process of the present invention canbe used to produce products suitable for ink jet coating applicationsfrom hydrous kaolin of different particle size distributions, calcinedclay and other mineral compositions such as ground calcium carbonate(GCC), precipitated calcium carbonate (PCC), bentonite and talc.

EXAMPLE 3

Hydrous kaolins of different particle size distributions and type(KAOFINE 90, KAOBRITE 90 and KAOWHITE S) are ground using a HSA -1attritor at 1200 RPM, 2400 ml zirconium silicate media (2-2.5 mm), 10Lb/hr feed rate and with 0.6 mm discharge screen size (100% open).Kaofine 90 is a Fine No.1 clay. Kaobrite 90 is a high brightness No. 2clay, while Kaowhite S is a standard brightness delmainated clay. Theproduct characteristics before and after grinding are compared in TableIII, and the ink jet printability is given in Table IV. The ink jetprintability of the products of this invention is also compared againstcommercially used silica pigments.

TABLE III Kaofine 90 Kaobrite 90 Kaowhite S Unground Ground UngroundGround Unground Ground BET Surface area (m²/g) 21.7 35.5-46.2* 16.6 36.714.5 49.0 Particle size, % <5.0μ 98.5 63.0 96.9 62.9 97.0 67.3 <2.0μ98.2 37.8 85.6 36.4 82.4 43.3 <1.0μ 98.2 27.8 73.5 24.1 63.8 28.5 <0.5μ91.9 18.3 56.2 13.8 41.6 15.7 <0.2μ 48.0 6.8 27.3 6.8 19.4 4.3 Mercuryintrusion Pore volume, ml/g 0.28 0.45-0.48* 0.31 0.45 0.34 0.44 **Poresize, nm 56  724-1351* 62 & 469 851 62 & 337 586 Scattering coeff. (457nm) 0.4911 0.2626 0.3593 0.2566 0.4053 0.2693 *Range for severalproducts ground at different times. **Dominant pore size

For each clay type, the data presented in Table III indicate thatsurface area particle size, pore volume and pore size (diameter)increase, while scattering coefficient decreases with grinding. Theseproperties are comparable to each other for all the ground products.

The data in Table IV show that the ground products are improved in colordensity, ink drying and image formation over the unground products.Table IV also shows that the print qualities of the pigments of thisinvention are highly comparable to silica coatings. In addition, thecoating colors using the pigments of this invention can be made down atmuch higher solids as compared to silica.

The binder (polyvinyl alcohol) requirement is much lower for thepigments of our invention (13 parts or less) than for silica (30 partsor higher). Also, the presence of a pigment of our invention decreasesthe binder requirement for silica. For example, one skilled in the artwould expect that a 50/50 mixture of silica and a pigment of thisinvention would have a binder requirement of about 21.5 parts (30 partsfor the silica portion and 13 parts for our pigment =21.5 parts at50/50). However, due to the presence of our pigment, the binderrequirement for a 50/50 mixture is only 13 parts or lower.

TABLE IV Coating Formulations Kaofine 90 100 — — — — — — — Kaofine 90,Ground — 100 100 — — — — — Kaobrite 90 — — — 100 — — — — Kaobrite 90,Ground — — — — 100 — — — Kaowhite S — — — — — 100 — — Kaowhite S, Ground— — — — — — 100 — Precipitated silica, FK310 — — — — — — — 80 Fumedsilica, MOX 170 — — — — — — — 20 Polyvinyl alcohol 13 13 13 13 13 13 1330 MHPC — — 1 — — — — — Poly-DADMAC 5 5 5 5 5 5 5 0.5 Coating pH 5.7 5.96.1 6.2 6.0 5.8 6.1 4.9 Solids, % 45.2 44.0 43.0 42.1 43.0 40.7 47.327.9 Ink Jet Printability (Calendered sheets) (SoftNip Calendered @ 1Nip/side, 55 PLI at 160° F.) Color Density Cyan 1.36 1.59 1.59 1.34 1.551.26 1.52 1.44 Magenta 1.24 1.55 1.55 1.26 1.54 1.18 1.49 1.32 Yellow0.94 1.28 1.28 1.09 1.26 0.99 1.23 1.10 Black 2.01 1.33 1.26 1.62 1.341.75 1.30 1.42 Image Formation Very poor Good Good Very Poor Good VeryPoor Good Good Ink absorption * 5 3 2 5 3 5 3 1 * 1-best and 5-worst.PLI = Pressure Per Linear Inch

EXAMPLE 4

KAOCAL and a 25/75 blend of KAOCAL/KAOFINE 90 are ground following theprocedure described in Example 3 except that the feed rate for KAOCAL is7 Lb/hr. The product characteristics before and after grinding arecompared in Table V.

TABLE V 25/75 KAOCAL/KAOFINE Kaocal 90 Unground Ground Unground GroundBET Surface 16.6 23.2 21.0 41.2 area (m²/g) Particle size, % <5.0μ 96.066.5 98.3 60.3 <2.0μ 88.1 46.4 95.8 37.2 <1.0μ 73.1 38.5 90.5 27.9 <0.5μ16.7 26.2 72.3 18.5 <0.2μ 0 6.5 37.5 5.8 Mercury intrusion Pore volume,ml/g 1.1324 0.5042 0.3992 0.5419 *Pore size, nm 337 474 62 & 390 137 &1693 Scattering coeff. 1.2924 0.3642 0.6466 0.2741 (457 nm) *Dominantpore size

The data in Table V show that both the surface area and particle sizeare increased, while the scattering coefficient is decreased upongrinding. Additionally, the data in Table V show that the pore volumedecreases for 100 percent Kaocal upon grinding, while the pore volumeincreases for the Kaocal/Kaofine 90 blend upon grinding. The grindingprocess breaks the original low bulk density, high pore volume and highlight scattering aggregates of the calcined clay followed by instantre-aggregation of ground particles into larger and denser aggregates.The high degree of aggregation in the ground product can be seen in thescanning electron micrographs shown in FIGS. 3-4.

The ink jet printability data of the ground and unground products arecompared in Table VI. The ground products show a significant improvementin color densities (cyan, magenta, yellow and black) and imageformation. The grinding process effectively reduces the light scatteringof the calcined clay which, in turn, increases the color densities ofthe printed image.

TABLE VI Coating Formulations Kaocal 100 — — — Kaocal, Ground — 100 — —25/75 Kaocal/Kaofine 90 — 100 — 25/75 Kaocal/Kaofine 90, — 100 GroundPolyvinyl alcohol 13 13 13 13 Poly-DADMAC 5 5 5 5 Coating pH 5.2 7.4 5.95.8 Solids, % 37.6 42.5 43.0 44.0 Ink Jet Printability (UncalenderedSheets) Color Density Cyan 0.89 1.51 1.35 1.61 Magenta 0.89 1.44 1.141.51 Yellow 0.69 1.09 0.86 1.22 Black 1.75 1.30 1.82 1.38 ImageFormation Poor Good Poor Good Ink absorption* 3 3 5 3 *1—best and5—worst.

EXAMPLE 5

This example shows that 100% natural ground calcium carbonate (GCC; butnot ground according to this invention) and the blends of GCC and clay(KF90) can be ground by using the process of this invention to producepigments suitable for ink jet coating applications. Blends are preparedby mixing the appropriate amounts of each slurry followed by spraydrying. The 100% GCC and the blends are ground using the processdescribed in Example 3. The product characteristics of ground andunground samples are presented in Table VII. The characteristics ofground and unground KF90 are also given for comparison.

TABLE VII Ground Calcium 50/50 25/75 Kaofine 90 Carbonate (GCC) GCC/KF90GCC/KF90 (KF90) Unground Ground Unground Ground Unground Ground UngroundGround BET Surface area (m²/g) 8.7 12.1 17.2 25.2 19.5 30.5 21.7 46.2Particle size (%) <5.0μ 97.9 62 99.3 59.6 98.16 61.2 98.5 63.0 <2.0μ84.2 39.6 94.6 38.3 96.3 37.4 98.2 37.8 <1.0μ 57.2 25.7 76.9 25.5 85.624.4 98.2 27.8 <0.5μ 29.5 12.6 54.7 14.1 69.1 14 91.9 18.3 <0.2μ 10.23.9 25.1 2.5 35 3.1 48.0 6.8 Mercury intrusion Pore volume (ml/g) 0.27110.7287 0.2619 0.4486 0.2729 0.4511 0.2776 0.45 to 0.48 *Pore size, nm 74& 236 1349 62 861 56 727 56 1348 Scattering coeff. (457 nm) — — 0.34430.1882 0.4220 0.2046 0.4911 0.2626 *Dominant pore size

Grinding GCC using a HS A-1 attritor is extremely difficult due toscreen clogging. However, the problem is eliminated when the GCC/clayblend is used, indicating that the clay actually serves as a grindingaid for the calcium carbonate.

The pigment properties presented in Table VII indicate that surfacearea, particle size, pore volume and pore size increase with grinding.Surface area increases with increases in the Kaofine 90 level, while theparticle size of all the products are very similar to each other.Although the pore volume of 100% Kaofine 90 and the blend samples areessentially the same, the pore volume is much improved for 100% GCC.

Scanning electron micrographs (FIGS. 5-6) show that all of the groundproducts are highly aggregated, and the degree of aggregation increaseswith the clay level.

The data in Table VIII show that all of the ground products are improvedin color density, ink drying and image formation over the unground GCCand Kaofine 90 coatings. Also, the ground products are comparable to oneanother in print performance irrespective of the pigment type (carbonateor clay). The original unground GCC and Kaofine 90 coatings do not formproper images due to slower ink/ink solvent absorption as compared tothe ground pigment coatings.

TABLE VIII Coating Formulations 1 2 3 4 5 GCC 100 — — — — GCC, Ground —100 — — — 50/50 GCC/KF90, — — 100 — — Ground 25/75 GCC/KF90, — — — 100 —Ground Kaofine 90, Ground — — — — 100 Polyvinyl alcohol 13 13 13 13 13Poly-DADMAC 5 5 5 5 5 Coating pH 8.0 8.0 7.7 7.5 5.9 Solids, % 42.2 42.345.0 44.5 44.0 Ink Jet Printability (Soft Nip Calendered @ 1 Nip/side,55 PLI at 160° F.) Color Density Cyan 1.27 1.56 1.56 1.58 1.59 Magenta1.26 1.51 1.57 1.55 1.55 Yellow 1.05 1.16 1.28 1.28 1.28 Black 1.18 1.351.28 1.29 1.33 Image Formation Very Poor Good Good Good Good Inkabsorption * 5 3 3 3 3 * 1-best and 5-worst. PLI = Pressure Per LinearInch

EXAMPLE 6

A precipitated calcium carbonate (PCC) and a 25/75 blend of PCC/KAOFINE90 are ground following the procedure described in Example 3, exceptthat the feed rate for PCC is 7 Lb/hr. The feed rate has to be loweredfor 100% PCC because of poor flowability from the grinding chamber. Theproduct characteristics before and after grinding are compared in TableIX.

The pigment properties presented in Table IX indicate that surface area,particle size, pore volume and pore size increase with grinding, whilescattering coefficient decreases. Scanning electron micrographs (FIGS.7-8) show that the ground products are highly aggregated.

TABLE IX 25/75, PCC PCC/Kaofine 90 Unground Ground Unground Ground BETSurface area 11.4 19.2 19.7 42.3 (sq. m/g) Particle size, % <5.0μ 99.860.6 99.9 62.6 <2.0μ 98.4 41.1 98.9 40.7 <1.0μ 92.0 32.2 96.4 31.7 <0.5μ65.2 20.3 82.1 21.5 <0.2μ 16.6 4.3 36.7 5.1 Mercury intrusion Porevolume, ml/g 0.2317 0.5076 0.2758 0.4110 *Pore size, nm 69 & 131 1685 62590 Scattering coeff. 0.4201 0.1483 0.4687 0.2087 (457 nm) *Dominantpore size

The data in Table X show that all of the ground products are improved incolor density, ink drying and image formation over the unground PCC.

TABLE X Coating Formulations Precipitated Calcium Carbonate 100 — — —(PCC) Precipitated Calcium Carbonate — 100 — — (PCC), Ground 75/25PCC/Kaofine 90 — 100 — 75/25 PCC/Kaofine 90, Ground — 100 Polyvinylalcohol 13 13 13 13 Poly-DADMAC 5 5 5 5 Coating pH 7.4 7.8 7.7 7.1Solids, % 36.7 46.1 44.1 43.1 Ink Jet Printability Color Density Cyan1.42 1.54 1.35 1.60 Magenta 1.26 1.54 1.18 1.53 Yellow 0.90 1.25 0.951.28 Black 1.60 1.35 1.72 1.37 Image Formation Poor Good Poor Good Inkabsorption* 5 3 5 3 *1—best and 5—worst.

EXAMPLE 7

A sample of sodium bentonite is ground at the same conditions asspecified in Example 3. The nitrogen surface area of the bentoniteincreases from 65.8 m²/g to 74.7 m²/g, and the mercury intrusion porevolume increases from 0.1696 to 0.2846 ml/g after grinding. The particlesize also becomes coarser as compared to the starting feed; for example,60% at <1 μm and 47% at <0.2 μm versus 58% at <1 μm and 27% at <0.2 μmof the ground material. As would be shown in a scanning electronmicrograph, the ground product is highly aggregated.

The ink jet printability results of ground and unground bentonite aregiven in Table XI.

TABLE XI 1 2 3 Coating Formulations Bentonite 100 — — Bentonite, Ground— 100 100 Polyvinyl alcohol 13 13 13 Poly-DADMAC — — 5 Coating pH 8.08.0 7.5 Solids, % 15 30.0 30 Ink Jet Printability (Uncalendered) ColorDensity Cyan 1.39 1.42 1.46 Magenta 1.31 1.35 1.35 Yellow 1.05 1.03 1.03Black 1.50 1.52 1.52 Image Formation/Acuity Poor Good Good Inkabsorption* 4 3 2 *1—best and 5—worst.

The printability of the ground product is improved over the ungroundstarting bentonite. The starting sodium bentonite swells in water andbecomes very viscous, and consequently the coating color can be madedown at 15% or lower solids only, while the ground bentonite productcoating color can be made down at 30% solids. The swelling effect of thestarting material is minimized or eliminated after grinding.

EXAMPLE 8

A sample of talc is ground by the process of Example 3. The pigmentcharacteristics of unground and ground talc and ground blends of talcand clay are shown in Table XII. The surface area and the degree ofaggregation increases after grinding for 100% talc and the 25/75talc/clay blend. However, the particle size of ground talc is smallerthan the starting material, because the starting material consists ofpredominantly large platy particles and appears very coarse bySedigraph.

TABLE XII Talc 25/75 Talc/Kaofine 90 Ground Ground Ground Unground OnceTwice Unground Once BET Surface 7.7 67.7 83.5 17.3 45.3 area (m²/g)Particle size, % <5.0μ 67.9 82.7 71.8 92.1 71.1 <2.0μ 29.6 62.7 50.681.3 44.9 <1.0μ 12.5 56.6 37.8 76.3 31.9 <0.5μ 2.9 28.9 25.2 68.9 20.9<0.2μ 0.5 10.3 8.7 33.4 8.1 Mercury intrusion Pore volume, 0.3945 0.54260.5426 0.3093 0.5497 ml/g *Pore size, 592 296 720 54 54, 390 & nm 1050Scattering 0.2709 0.3692 0.2607 0.3510 0.2773 coefficient (457 nm)*Dominant pore size

The large plates are broken down followed by aggregation after grinding,but the aggregates are still smaller than the particle size of thestarting material (see FIGS. 9-10). The product ground twice shows ahigher degree of aggregation than the product ground once.

The ink jet printability data are given in Table XIII. The colordensity, drying and image formation improve after grinding. The 100%talc has to be ground twice to obtain an overall improved product.

TABLE XIII Coating Formulations Talc (unground) 100 — — Talc (Groundonce) — 100 — Talc (ground twice) 100 75/25 KF 90/Talc — — — 100 (groundonce) Polyvinyl alcohol 13 13 13 13 Poly-DADMAC 5 5 5 5 Coating pH 8.27.8 8.2 7.8 Solids, % 44.5 45.0 42.6 44.0 Ink Jet Printability (Soft NipCalendered @ 1 Nip/side, 55 PLI at 160° F.) Color Density Cyan 1.16 1.451.47 1.53 Magenta 1.16 1.40 1.37 1.49 Yellow 0.97 1.07 1.06 1.20 Black1.80 1.62 1.45 1.39 Image poor poor good good Formation/Acuity Ink 4 3 33 Absorption/Drying* *1—best and 5—worst. PLI = Pressure Per Linear Inch

Example 9

This example demonstrates that acid leaching can further increase thesurface area of the products of this invention.

Various unground and ground products are treated with a mineral acidsuch as sulfuric acid at various concentrations, temperatures andperiods of time. The product type, acid treatment condition and thesurface area of the products are given in Table XIV. The data show thatthe product of this invention can be treated with an acid to furtherincrease the surface area, while the original hydrous kaolin (KAOFINE90) fully calcined clay (KAOCAL), bentonite and talc do not respond tothis treatment in a significant way. For example, surface area oforiginal KAOFINE 90 only increases from 21.7 m²/g to 24.7 m²/g afteracid treatment, while the surface area of the ground product increasesfrom 49.9 m²/g to as high as 219 m²/g upon acid treatment.

TABLE XIV Surface Area No. Sample Type/Treatment Conditions (m²/g) 1Original KAOFINE 90 (no treatment) 21.7 2 No. 1 treated with acid 24.7(1M acid, 4 hr, 90° C.) 3 KAOFINE 90 ground @ 1100 RPM, 2000 ml media49.9 volume and 6.5 Lb/hr feed rate 4 No. 3 treated with acid (1M acid,1 hr, 60° C.) 113 5 No. 3 treated with acid (1M acid, 4 hr, 60° C.) 1356 No. 3 treated with acid (1M, 1 hr, 90° C.) 119 7 No. 3 treated withacid (1M acid, 4 hr, 90° C.) 174 8 No. 3 treated with acid (pH = 2, 1hr, 60° C.) 67.3 9 No. 3 treated with acid (0.5M, 4 hr, 90° C.) 124 10No. 3 treated with acid 219 (5M, 2 hr at Room Temp, and 2 hr at 90° C.)11 Original KAOCAL (no treatment) 16.6 12 No. 11 treated with acid 21.7(1M acid, 4 hr., 90° C.) 13 KAOCAL ground @ 1100 RPM, 2000 ml media 27.4volume and 6.5 Lb/hr feed rate 14 No. 13 treated with acid 50.6 (1Macid, 4 hr., 90° C.) 15 Metakaolin (no treatment) 22.5 16 No. 15 treatedwith acid 150 (1M acid, 4 hr., 90° C.) 17 No. 15 treatment with acid 391(5M acid, 4 hr., 90° C.) 18 Metakaolin ground @ 1100 RPM, 2000 ml media19.1 volume and 6.5 Lb/hr feed rate 19 No. 18 treated with acid 92.1 (1Macid, 4 hr., 90° C.)

The present invention has been described in detail with particularreference to certain embodiments, but variations and modifications canbe made without departing from the spirit and scope of the invention asdefined in the following claims.

What is claimed is:
 1. A process for treating mineral compositions,wherein the process comprises the sequential steps of: A. obtaining abeneficiated, unground mineral composition starting material; and B. drygrinding the starting material under conditions of high intensitysufficient to aggregate the ground material, whereby the surface area ofthe ground material is increased over the surface area of the ungroundstarting material.
 2. A process as defined by claim 1 wherein theunground starting material is hydrous kaolin clay, calcined kaolin clay,natural calcium carbonate, precipitated calcium carbonate, calciumsulfate, aluminum hydroxide, bentonite, talc or a mixture of two or moreof these materials.
 3. A process as defined by claim 2 wherein theunground starting material is hydrous kaolin clay.
 4. A process asdefined by claim 2 wherein the unground starting material is calcinedkaolin clay.
 5. A process as defined by claim 2 wherein the ungroundstarting material is calcium carbonate.
 6. A process as defined by claim2 wherein the unground starting material is bentonite.
 7. A process asdefined by claim 2 wherein the unground starting material is talc.
 8. Aprocess for treating mineral compositions, wherein the process comprisesthe sequential steps of: A. obtaining a beneficiated, unground mineralcomposition starting material; B. dry grinding the starting materialunder conditions of high intensity sufficient to aggregate the groundmaterial; and C. subjecting the ground material to an acid treatment,whereby the surface area of the acid-treated, ground material isincreased over the surface area of the ground starting material prior toacid treatment.
 9. A process as defined by claim 8 wherein the ungroundstarting material is hydrous kaolin clay, calcined kaolin clay,bentonite, talc or a mixture of two or more of these materials.
 10. Anaggregated mineral pigment having increased surface area wherein thepigment is produced by a process comprising the sequential steps of: A.obtaining a beneficiated, unground mineral composition startingmaterial; and B. dry grinding the starting material under conditions ofhigh intensity sufficient to aggregate the ground material, whereby thesurface area of the ground material is increased over the surface areaof the unground starting material.
 11. A pigment as defined by claim 10wherein the unground starting material is hydrous kaolin clay, calcinedkaolin clay, natural calcium carbonate, precipitated calcium carbonate,calcium sulfate, aluminum hydroxide, bentonite, talc or a mixture of twoor more of these materials.
 12. An aggregated mineral pigment havingincreased surface area wherein the pigment is produced by a processcomprising the sequential steps of: A. obtaining a beneficiated,unground mineral composition starting material; B. dry grinding thestarting material under conditions of high intensity sufficient toaggregate the ground material; and C. subjecting the ground material toan acid treatment, whereby the surface area of the acid-treated, groundmaterial is increased over the surface area of the ground startingmaterial prior to acid treatment.
 13. A pigment as defined by claim 12wherein the unground starting material is hydrous kaolin clay, calcinedkaolin clay, bentonite, talc or a mixture of two or more of thesematerials.
 14. A coating pigment produced by a process which comprisesthe sequential steps of: A. obtaining a beneficiated, unground mineralcomposition starting material; and B. dry grinding the starting materialunder conditions of high intensity sufficient to aggregate the groundmaterial, whereby the surface area of the ground material is increasedover the surface area of the unground starting material.
 15. A coatingpigment as defined by claim 14 wherein the unground starting material ishydrous kaolin clay, calcined kaolin clay, natural calcium carbonate,precipitated calcium carbonate, calcium sulfate, aluminum hydroxide,bentonite, talc or a mixture of two or more of these materials.
 16. Acoating pigment produced by a process which comprises the sequentialsteps of: A. obtaining a beneficiated, unground mineral compositionstarting material; B. dry grinding the starting material underconditions of high intensity sufficient to aggregate the groundmaterial; and C. subjecting the ground material to an acid treatment,whereby the surface area of the acid-treated, ground material isincreased over the surface area of the ground starting material prior toacid treatment.
 17. A pigment as defined by claim 16 wherein theunground starting material is hydrous kaolin clay, calcined kaolin clay,bentonite, talc or a mixture of two or more of these materials.
 18. Apigment for an ink jet coating application, wherein the pigment isproduced by a process which comprises the sequential steps of: A.obtaining a beneficiated, unground mineral composition startingmaterial; and B. dry grinding the starting material under conditions ofhigh intensity sufficient to aggregate the ground material, whereby thesurface area of the ground material is increased over the surface areaof the unground starting material.
 19. A pigment as defined by claim 18wherein the unground starting material is hydrous kaolin clay, calcinedkaolin clay, natural calcium carbonate, precipitated calcium carbonate,calcium sulfate, aluminum hydroxide, bentonite, talc or a mixture of twoor more of these materials.
 20. A pigment for an ink jet coatingapplication, wherein the pigment is produced by a process whichcomprises the sequential steps of: A. obtaining a beneficiated, ungroundmineral composition starting material; B. dry grinding the startingmaterial under conditions of high intensity sufficient to aggregate theground material; and C. subjecting the ground material to an acidtreatment, whereby the surface area of the acid-treated, ground materialis increased over the surface area of the ground starting material priorto acid treatment.
 21. A pigment as defined by claim 20 wherein theunground starting material is hydrous kaolin clay, calcined kaolin clay,bentonite, talc or a mixture of two or more of these materials.